The long-term objective of this application is to understand how EFEMP1 is involved in the pathogenesis of Doyne honeycomb retinal dystrophy (DHRD) and Malattia Leventinese (ML). A characteristic feature of DHRD/ML is the presence of drusen beneath the retinal pigment epithelium (RPE). Little is known about the composition or formation of drusen. A single mutation (R345W) in the gene EFEMP1 was found to be responsible for DHRD/ML. EFEMP1 is an uncharacterized protein of unknown function. The preliminary results of this application indicate that EFEMPI is a secreted protein and that EFEMP1R345W accumulates within cells and is secreted less efficiently than wild type EFEMP1. In the retina of a ML patient homozygous for the R345W mutation, EFEMP1 was found to accumulate in the RPE and the RPE basement membrane region immediately overlaying drusenoid deposits. No such accumulation was noted in the eyes of healthy human donors. Thus the hypothesis of this application is that EFEMP1R345W is involved in drusen formation through the impairment of trafficking by EFEMP1R345W aggregates between Bruch's membrane and RPE cells and/or within RPE cells. Guided by this hypothesis, the specific aims focus on: expression of the EFEMP1 protein in normal and pathological tissues, determine how the R345W mutation results in the accumulation of EFEMP1 within and beneath RPE cells, and identification of molecules interacting with EFEMP1. The studies outlined in this application should aid in understanding how this gene defect leads to the retinal pathology associated with DHRD/ML and developing effective intervention and beneficial medical treatment protocols for DHRD/ML. The expression of EFEMP1 protein in normal and pathological retina tissues will be determined by immunohistochemistry and immunoelectron microscopy. The effect of the R345W mutation on the fate of EFEMP1 protein will be determined through the comparison of the trafficking of EFEMP1 and EFEMP1R345W in RPE cells and the study on the mutation's effect on the proteasome degradation system and turnover process of EFEMP1 in RPE cells. Proteins interacting with EFEMP1 will be identified by immunoaffinity purification of EFEMP1 complexes followed by mass spectrometry. The effect of the R345W mutation on these interactions will be tested using recombinant EFEMP1R345W.